Abstract

The collection of bacteria, viruses, and fungi that live in and on the human body, collectively known as the microbiome, has recently emerged as an important factor in human physiology and disease. The gut in particular is a biological niche that is home to a diverse array of microbes that influence nearly all aspects of human biology through their interactions with their host; new technologies are beginning to reveal important aspects of host-microbe interactions. Articles in this Review series address how perturbations of the microbiota, such as through antibiotic use, influence its overall structure and function; how our microbiome influences the impact of infectious agents, such as C. difficile; how our microbiome mediates metabolism of xenobiotics; how the microbiota contribute to immunity as well as to metabolic and inflammatory diseases; and the role of commensal microbes in oncogenesis.

Authors

Figure 1

In this global model, the microbiome affects physiologic functions at each life stage as a participant in life cycle events and processes. During early life development, as the microbiome transforms, it gains diversity and complexity, maturing into an adult-type pattern. This transformation occurs in parallel with host metabolic, immunologic, and cognitive development and undoubtedly contributes to normal physiology. Perturbation could thus have important deleterious consequences. After reproductive life wanes, the selection on the microbiota differs, with important consequences for diseases. I hypothesize that the changed selection fuels the descent into the degenerative and neoplastic diseases of aging.